1. Field of the Invention
The invention relates to a process for decaffeinating green coffee beans in which caffeine is removed from the green coffee beans by means of a supercritical fluid which is gaseous under standard conditions of temperature and pressure, i.e., 1 bar, 20.degree. C.
2. Background of the Art
Many individuals cannot tolerate whole coffee because of its caffeine content. Numerous processes have therefore been developed to extract caffeine from the coffee while avoiding removal of other substances which are needed to create aroma during roasting of the beans and/or brewing of the beverage. When caffeine is removed from green coffee beans, loss of aroma cannot be avoided.
In one traditional decaffeinating process, green coffee beans are subjected to a pretreatment step, e.g., decomposition of the coffee beans by steam at high temperature; then leached by solvents such as di- or trichloroethylene to remove caffeine; treated to remove solvent from the leached green coffee beans through evaporation; and dried to remove moisture. This known process, however, does not preclude solvent residues remaining in the coffee and occurance of a certain denaturation of the green coffee beans.
Processes have also been suggested using extraction solvents which are supercritical fluids, that is, substances at a high temperature and pressure which are neither in the liquid state nor the gaseous state, but are in a state of matter in which they exhibit the properties of both liquids and gases. In such processes, long extraction times are typically required to achieve sufficient decaffeination. This is due to the fact that the caffeine must first diffuse to the surface of the coffee beans so that it can be absorbed by the solvent. This process slows down further as caffeine concentration in the coffee beans is reduced. In many of these known processes, the solvent is cycled during extraction requiring high capital equipment investment and high energy costs.